iommu/tegra: gart: Perform code refactoring

Removed redundant safety-checks in the code and some debug code that
isn't actually very useful for debugging, like enormous pagetable dump
on each fault. The majority of the changes are code reshuffling,
variables/whitespaces clean up and removal of debug messages that
duplicate messages of the IOMMU-core. Now the GART translation is kept
disabled while GART is suspended.
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>